Thursday, June 14, 2007
Martian Ocean Mystery Solved? Dwarf Planet Eris Bigger Than Pluto.
Today I have two stories to present from the Yahoo News Space.com section. The first deals with evidence that Mars once had large oceans , and also deals with how the determination that Mars even HAD oceans was made, and the phenomenon that may have worked in tandem to cause Mars to lose most of the water. The second story deals with the determination that Dwarf Planet Eris, discovered in 2005, is larger than Pluto. Read on...
Martian Oceans Mystery
Since 1991, planetary scientists have floated the idea that Mars once harbored vast oceans that covered roughly one-third of the planet. Two long shore-like lips of rock in the planet's northern hemisphere were thought to be the best evidence, but experts argued that they were too "hilly" to describe the smooth edges of ancient oceans.
The view just changed dramatically with a surprisingly simple breakthrough. The once-flat shorelines were disfigured by a massive toppling over of the planet, scientists announced today. The warping of the Martian rock has hidden clear evidence of the oceans, which in any case have been gone for at least 2 billion years.
"This really confirms that there was an ocean on Mars," said Mark Richards, a planetary scientist at the University of California at Berkeley and co-author of the study, which is detailed in the June 14 issue of the journal Nature.
Two major shorelines exist on Mars, each thousands of miles long--one remaining from the older Arabia Ocean, and another from the younger Deuteronilus Ocean, said study co-author Taylor Perron of UC Berkeley. "The Arabia would have contained two to three times the volume of water than in the ice that covers Antarctica," Perron told SPACE.com.
Somewhere along the way to toppling over 50 degrees to the north, Mars probably lost some of its water, leaving the Deuteronilus Ocean's shoreline exposed. "The volume of water was too large to simply evaporate into space, so we think there is still some subterranean reservoirs on Mars," Perron said. The remaining sea would have been located in the same lowland plain as the Arabia Ocean, but almost 40 degrees to the north.
As a planet spins, the heaviest things tend to shift towards the equator, where they are most stable. Earth, too, has a bulge at its equator. The volcanic Tharsis region of Mars, a vast raised area along Mars' equator, is evidence for how this works.
"On planets like Mars and Earth that have an outer shell ... that behaves elastically, the solid surface will deform," Richards said. By calculating the deformation, which occurs in a predictable way, the planetary research team found the ridges had to have once been flat, like ocean shorelines.
Perron and his colleagues aren't certain what caused the toppling of the planet, but they think forces beneath the surface are to blame. "There could have been a massive change in the distribution of mantle," Perron said, "which would have caused the planet to shift into its current position."
One reason may be that Mars does not have the good fortune to have a large moon, like we Earthlings do. Our Moon is large enough, that given the types of forces described in the last paragraph, it can counter most of the momentum shift and stabilize us before the continents and oceans go shifting all over the place. Mars has two moons, Phobos and Deimos, both of which are no bigger than mountains here on Earth, and which have a negligible gravitational effect on their primary.
Dwarf Planet Eris Larger than Former Planet Pluto
The dwarf planet that effectively forced astronomers to strip Pluto of its planethood is not only bigger than the former ninth planet, but also much more massive, a new study finds.
Michael Brown, a planetary scientist at Caltech, and his graduate student Emily Schaller have determined that Eris, discovered in 2005 by Brown and his team, is about 27 percent more massive than Pluto. The finding, detailed in the June 15 issue of the journal Science, also confirms Eris and Pluto have similar compositions.
Eris circles the sun from about 9 billion miles away-about twice the distance of Pluto at the farthest point in its orbit. Its discovery was one of several factors that led some astronomers to create a new definition for planethood at the 2006 meeting of the International Astronomical Union (IAU) in Prague. The ruling reduced the planet count in our solar system to eight and left Pluto renamed as a "dwarf planet."
To determine Eris' mass, the researchers used the Hubble Space Telescope and the Keck Observatory to calculate the orbital speed of its moon, Dysnomia. According to Newtonian physics, the more massive a celestial object is, the faster its satellite will zip around it. "By looking at the time it takes the moon to go around Eris, we're able to calculate the mass," Schaller said.
Because Eris and Dysomnia are located more than 90 times farther from the sun than Earth--out in the Kuiper Belt region of the solar system, they appear as little more than pricks of light in telescope observations. "Eris is slightly larger than a point source, but just barely," Schaller said.
Dysnomia is thought to be less than 100 miles (150 km) across and to take about 16 Earth-days to make one trip around Eris.
Eris itself is believed to have a diameter of 1,490 to 1,860 miles (2,400 to 3,000 km). "To put that into perspective, if you took all the asteroids in the asteroid belt [between Mars and Jupiter] and multiplied by four, they would easily all fit into Eris," Schaller told SPACE.com.
Pluto has a diameter of about 1,430 miles (2,300 km) across.
Knowing Eris' mass and size, the researchers were also able to confirm that Eris' density is similar to that of Pluto, and that it is therefore likely made up mainly of rock and water ice.
Not much too add here, except to say that "demoting" Pluto seems not to have been such a silly idea after all. And I'd be willing to bet that there are more Eris-sized (or larger) bodies out there in the Kuiper Belt.